1. Technical Field of the Invention
The invention relates to improvements in harvesting machines. In particular, the invention relates to improvement in the automatic leveling of harvester shaker screens where the harvested seed, etc., is separated from straw, and chaff.
2. Prior Background Art
When a harvesting machine moves through a field, it plucks the produce--grain, corn, etc.--and deposits it, eventually, on a screen along with various vegetative wastes, referred to herein generally as "chaff." The grain, corn, etc., hereinafter referred to generally as "seed," passes through the screen to be accumulated as part of the days harvest. The chaff falls over the end of the screen to be returned to the field. Efficiency demands that little, and preferably none, of the seed shall be contained in the chaff returned to the field.
The screen is on a shaker bed. The bed vibrates the screen to improve the efficiency of the screening action. The harvester, itself, is a well organized machine. It travels at a speed which enables it to pick just enough seed to be transferred to the screen without overflowing the screen. The driver is in control of the harvester and experiences little challenge in maintaining proper speed so long as the field is level. Problems can arise, however, when the field is not level.
When the harvester travels a level field, material to be screened by the shaker screen will cover the screen surface fairly uniformly, However, with even a slight slope in the field there is a tilt imparted to the shaker screen and the material accumulates on the "down hill" portion of the screen. This decreases the efficiency of the screening action since a part of the screen is NOT being utilized.
The practical effect of working a harvester on a slope is the necessity of reducing the speed at which the harvester travels through the field, as compared to its speed over a level field. The slower speed is required to permit the seed, accumulated now on only a portion of the screen surface, to pass through the screen, rather than be ejected with the chaff.
Reducing the speed of harvester travel through the field means that the rate at which the harvest is achieved is reduced as well. More fuel is used because more days of working are required to complete the harvest. In general, there will be a lower yield from a sloping field directly attributable to the slower speed of harvest. The longer a ripe crop is allowed to remain in the field, the more "fruit" that drops to the ground, and the more plants that droop and fall to be missed by the passing harvester.
Such losses in efficiency can, conceivably, be obviated by the simple expedient of maintaining the shaker screen in a level plane regardless of the disposition of the harvester. But, with the large screen generally employed, too much space above and below the screen must be reserved within the harvester to accommodate the arc travel of the edge of the screen. If several smaller screens are used, instead of one large screen, the arc traveled by the edge of the smaller screen is less than that of the larger screen for a given angle of tilt.
A plurality of smaller, tilting screens was the solution taught by E. W. Bozarth in U.S. Pat. No. 2,500,448, issued Mar. 14, 1950. His solution, however, required that each individual screen be coupled to its neighbor and that all be coupled to a pendulum mass mounted exterior of the harvester. The solution could not be easily applied, retroactively, to an existing harvester. Physical changes to the harvester body were necessitated with the installation of Bozarth' tilting screens on the harvester. Once installed, a major effort was required to remove the installation.
It is the intent of the present invention to improve upon the prior art teachings re the use of self leveling, multiple, shaker screens on a harvester. It is intended that the present invention will be readily installed and removed from a harvester with relative ease; that no significant modifications will need to be made to the harvester to allow the installation of the invention; and, that the original, non-leveling shaker bed may be readily reinstalled on the harvester when desired.